Blading for turbines and like machines



A. G. SMITH June 12, 1956 BLADING FOR TURBINES AND THE LIKE] MACHINESFiled Oct. 5, 1948 R O m V W.

us'lz eo/)'efim BY Mm, www ATTORNEYS United States Patent O BLADING FORTURBINES AND LIKE MACHINES Application october s, 194s, seria1N0..5z,s1s1 Claims priority, application Great Britain October 28, 1947 4 Claims.(Cl. 25339.15)

This invention relates to improvements in blading for turbines andsimilarly bladed rotary machines, and is concerned more particularly,though not exclusively with turbine blading of combustion gas turbines.

The object of the present invention, stated in general terms, is toprovide improved means for cooling blading of turbines and similarlybladed rotary machines which is required to be subjected to mechanicallyundersirable high temperatures.

Especially in relation to gas turbines, the practicable workingtemperature of the rotor blading is frequently a limiting factor in theperformance of the machine, and it is possible to design a given machinefor higher performance if the blading is effectively cooled;alternatively, for a machine of given performance, longer life may beachievable and it may be possible to use lower grade metal for theblading. Moreover, in high temperature turbines employing blade coolingit is advantageous to run at tip speeds higher than those normallyconsidered economic for static gas turbine powerV plant, since it isdesirable to limit the number of stages in order to minimise heat lossesto the cooling fluid. In no practicable circumstances can the heat inthe cooling fiuid be used so efficiently as it would have been if leftin the working fluid. It follows, therefore, that it is an advantage tobe able to use a blade fixing which for a given turbine speed has thelowest possible maximum permissible stress, a factor which isconsiderably influenced by the effectiveness of the cooling.

The invention is concerned with that class of blade cooling system inwhich a blade to be cooled has an internal cavity through which there isa flow of coolant fluid by which heat is taken off. Y

According to the invention a blade cooling system of the class referredto comprises means which provide for a concentration of heat exchangesurface in the internal cavity of a blade to be cooled, that is, for asurface which affords an increased effective heat exchange surface perunit of projected area as compared with a plane surface.

According to a further feature of the invention, such heat exchangesurface is provided by means of a filling or matrix within the bladecavity, which matrix is preferably in heat conducting relationship withthe wall of the cavity and may be composed of material such as metalfoil, wire, wire wool or the like. To achieve good thermal connectionbetween the matrix and the wall of the cavity the matrix may be suitablybonded to said wall, as for example by brazing.

By suitable choice of the wall thickness of the blade, a design may beachieved which is not appreciably inferior in strength to a solid blade,whilst a matrix of foil or similar material may have an area severaltimes as great as that of the surface of a simple cavity Within theblade, so that the internal coolant flow may be at a relatively lowspeed, involving correspondingly small losses in pressure andincidentally reducing or eliminating the need to use an auxiliary pumpfor supplying the coolant.

The invention is primarily intended for use in a system employing ascoolant an air flow entering at the root of g 2,750,147 Patented June12,

which:

Figure 1 is a transverse section through one form of blade according tothe invention;

Figure 2 is a similar view of a second form;

Figure 3 is a transverse section of a third form.

Figure 4 is a similar view of a fourth form.

Figure 5 is a longitudinal section on the camber line V-V of theformshown in Figure 4.

Figure 6 shows a method of attaching a blade to a turbine disc.

Figure 7 shows an arrangement for supplying coolant fiuid to' a turbinedisc and blade.

In Figure l a turbine rotor blade 1 has a thin wall 2 of relativelyuniform thickness, enclosing a single cavity 3 extending longitudinallyof the blade which in this case may be manufactured by welding togethertwo separate elements forming its two faces and subsequently machiningto the required thickness and shape. A filling or matrix 4 consisting ofan air-permeable mass of metallic material which may for example becopper foil and may be formed to shape in a variety of ways is then'inserted into the cavity 3, such insertion being from either endin thecase vof a blade of constant thickness or from the root endv in the caseof a tapered blade. The foil 4 is then bonded to the blade wall 2, forexample by furnace brazing, to produce an intimate thermal connectiontherewith. Alternatively, as shown in Figure 2, the lfilling or matrix 4may be' ot copper Wool, which is preferable in some circumstances sinceit can be inserted through the thin end of a tapered blade and wouldoffer the aero-dynamic advanta-ge of permitting chord-wise flow -of thecoolant. If desired, in either case, an inner core 30 may be insertedwith the matrix 4 in order to fill up the aerodynamically less usefulcentral portion of the blade cavity 3.

In Figure 3 the blade 1 has a number of longitudinal passagesv 5 formedtherein either by drillingV a solid blade, or during the course ofmanufacture in the case of blades made by casting or by powdermetallurgy technique. lIn this case each passage 5 contains its ownfilling or matrix 4 which is bonded to the wall of the passage or cavity5.

As described below with reference to Figure 7, each blade cavity isassociated with a blade root mounting provided with air entry passagesby which cooling air is led to the interior of the blade, the air beingled out of the blade as may be most convenient, for example, through adownstream facing nozzle 27 or through holes 26 in a blade end cap 25.

In Figure 4 the cooling arrangement is combined with the so-calledblanket system of cooling a blade. In the latter system, cooling air issupplied to the surface of a blade in such a way as to form thereon acool boundary layer. Theoretically, such a system allows the entireblade surface to be kept at the temperature of the boundary layer, butin practice it is ditiicult to ensure satisfactory cooling of theleading edge. According to another feature of the invention it istherefore proposed to cool the leading edge portion of a bladeseparately and to use blanket cooling for the remainder of the blade.

Thus in Figure 4 the leading edge portion 6 of a blade has alongitudinal passage or cavity 7 therein containing a filling or matrix8 bonded to the wall of cavity 7 and supplied with cooling air throughthe blade root. Immediately downstream of the part 6 the remaining part13 of the blade has longitudinal passage or cavity 9 which as shown inFigure 5 interconnects with the passage 7 at the tip end of the bladeand receives air emerging from passage 7 and discharges it downstreaminto the working fluid fiow through gaps 31 along both faces of the part13 as indicated by the arrows 32 in Figure 4. In this Case the blade isformed in two separate parts 6, 13 which are connected together at thetip by a tip portion 14. i

The effectiveness of the blade cooling achieved by the invention isexpected to be such as to allow the use of simpler forms of blademounting than those in current use in conditions in which the roottemperature is relatively high, since with an effectively cooled bladeit is possible so to reduce the root temperature that for givenconditions of speed the root mounting may be one for which the maximumpermissible stress is lower than would otherwise be the case.

Thus the blade may be devoid of any large root portion and asl shown inFigure 6 a blade 1 may be secured to a turbine disc 12 by entering theradially inner end 10 of the blade 1 into a slot 11 of correspondingshape milled or otherwise formed in the periphery of the rotor 12, theblade 1 being secured in the slot 11 for example by copper brazing. Aninlet passage 15 must, in this case, be pro- .annular space formedbetween the upstream face 22 of rotor 12 and an annular shield 21securedl to the rim of rotor 12 and rotating with said rotor. Passagesor inlets 15 lead from the space 20 to a transverse cavity 23 in theroot of the blade 1 and from here the air is led to longitudinalpassages 24 within the blade 1.

The air may be led out of the blade 1 through openings 26 or 27 in ahollow cap 25 at the tip of the blade into which the longitudinalpassages 24 lead.

I claim:

1. In a turbine, a blade mounted for operation in a high temperaturegaseous zone of the turbine, said blade having root and tip ends and aportion thereof defining an internal cavity, an inlet to said cavity atthe root end of said blade, said blade so defining said cavity that itcommunicates with said zone at the tip end of said blade, meansconnected to said inlet to deliver a coolant fluid thereto, and afluid-permeable mass of metallic material within said cavity, saidmaterial being bonded to the cavity defining portion of the blade.

2. In a turbine, a blade mounted for operation in a high temperaturegaseous zone of the turbine, said blade having root and tip ends and athin wall of relatively uniform thickness defining a single internalcavity extending 4 from the root to the tip of said blade with the tipend of said cavity open to said high temperature zone, an inlet to saidcavity at the root end of said blade, means connected to said inlet todeliver coolant fluid thereto; and a fluid-permeable mass of metallicmaterial within said cavity, said material being bonded to said definingwall.

3. In a turbine, a blade mounted for operation in a high temperaturegaseous zone of the turbine, said blade having root and tip ends and aportion thereof defining a plurality of internal cavities extending fromthe root to the tip of said blade, an inlet to each cavity at the rootend of said blade, said blade so defining said cavities that theycommunicate at their tip ends with said high temperature zone; meansconnected to said inlets to deliver coolant fluid thereto; and a fluidpermeable mass of metallic material within each said cavity, saidmaterial being bonded to the portion of said blade defining saidplurality of internal cavities.

4. In a turbine, a blade mounted for operation in a high temperaturegaseous zone of the turbine, said blade having root and tip ends and aleading edge, a portion of said blade defining an internal cavityextending from the root to the tip of the blade in the leading edgethereof, another portion of said blade defining a second internal cavityextending from the root to the tip of said blade immediately downstreamof the leading edge cavity, an inlet to said leading edge cavity at theroot end of said blade, said second internal cavity interconnecting withsaid first-mentioned internal cavity at the tip end of the blade, saidblade having apertures therethrough establishing passageways between thesecond cavity and the high temperature zone; means connected to saidinlet to deliver coolant fluid thereto and a fluid-permeable mass ofmetallic material within said leading edge cavity and bonded to theleading edge cavity defining portion of said blade.

References Cited in the file of this patent UNITED STATES PATENTS843,068 Brady Feb. 5, 1907 1,893,330 Jones Jan. 3, 1933 2,183,527 AlarieDec. 19, 1939 2,220,420 Meyer Nov. 5, 1940 2,236,426 Faber Mar. 25, 19412,297,446 Zellbeck Sept. 29, 1942 2,337,619 Miller Dec. 28, 19432,401,826 Halford June 1l, 1946 2,520,373 Price Aug. 29, 1950 FOREIGNPATENTS 22,028 Great Britain Nov. l, 1901 509,105 Great Britain July 11,1939 584,580 Great Britain Jan. 17, 1947 602,530 Great Britain May 28,1948

